It is often desirable to obtain different kinds of information about particles.
One kind of information is about shear stress. An existing method of detecting wall shear stress puts a heated wire or element in the flow to be detected. The rate of cooling of the element provides a measure of the wall shear stress. Other similar sensors, which sense other parameters, are also known.
However, this system by itself has certain problems. The techniques may be intrusive, meaning that they may effect the rate of flow. The techniques can be affected by contaminants in the flow. For example, certain contaminants may deposit on the heated element and cause the heated element to react differently. These techniques can also change the characteristics of the sensor; hence requiring calibration.
Non-intrusive optical techniques may be considered using conventional optics. However, this results in a bulky setup, and setup that is highly susceptible to vibration. Moreover, the size of such a setup may cause difficulty in allowing the system to be effectively used.
Other kinds of probes can be used to detect the size of particles, and may have similar drawbacks.